priate in specific nonattainment areas, especially if they were developed from a data base different from that used to build any of the other regulatory models associated with the ozone-compliance process.

Summary

Gasoline has been reformulated to adjust its basic properties for various reasons over a very long period of time, before, in fact, air quality became a major issue. The relatively recent emphasis on the control of ozone precursor emissions and toxic emissions has prompted a new and comprehensive gasoline reformulation strategy. This strategy involves: (1) reduction in summer volatility (expressed as RVP); (2) reduction in reactive gasoline components (e.g., olefins) during the summer to reduce the ozone-forming potential of motor-vehicle emissions; (3) reduction in benzene and other aromatic content of gasolines year-round, and (4) addition of oxygenates as a means to help control emissions and to maintain octane rating using nontoxic constituents. The first three of these are formally included in the federal and California reformulated gasoline programs.

The adoption and use of the Complex Model and Predictive Model have been driven by a need for establishment of a level playing field for all refiners, as well as an easy and inexpensive fuel certification procedure that allows mixing of different batches thereby facilitating fuel distribution. The models appear to meet those needs. However, the methods used in those models to predict the in-use performance of gasolines reformulated to meet the criteria of the reformulated gasoline programs, are based on results from large and diverse, but nonetheless limited, data bases. They might not accurately represent what actually occurs in specific nonattainment areas, especially where a high summer-temperature rise produces relatively high evaporative VOC emissions. They might even deny refiners the ability to formulate fuels that could be more beneficial on the basis of atmospheric reactivity—an issue that is addressed in Chapter 7.



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